The present invention relates to low voltage, high displacement piezoelectric ceramic actuators. These actuators are useful for such military and commercial applications as: vibration damping, noise suppression, acoustic camouflage, actuated structures and positioning. Additionally, these actuators may be grouped in multiple arrangements and operated simultaneously so that their force and strain outputs are additive, or grouped and operated individually, to achieve acoustic signal generation, e.g., in acoustic imaging or transmitting, or in acoustic communication.
In order to meet the requirements presented by such applications, piezoelectric actuators must exhibit both moderate-to-high displacement and moderate-to-high force. Thus far, piezoelectric actuators have been limited by the need to balance displacement and force requirements in the device. For example, the choice has been between low displacement with high force (monolithic or multilayer piezoelectric ceramic actuators) or high displacement with low force (piezoelectric benders and strain amplifiers). Little capability has existed for varying the force-displacement characteristics to suit a particular application.
Several types of piezoelectric devices have been developed to meet the need for high displacement actuation. These devices all increase the displacement at the expense of load carrying capability. In most of these devices, an additional performance penalty arises from energy losses in the strain amplification mechanism. Examples of such devices include piezoelectric benders, Inchworm motors, and flextensional actuators. Piezoelectric bender devices can exhibit high bending strain levels of up to 10%, but their load carrying capabilities are only on the order of 10.sup.-4 MPa. The Inchworm motor can exhibit large lateral displacements and reasonable loads, but its speed is limited. Flextensional actuators have been used as strain amplification devices for both single layer and multilayer piezoelectric materials, with typical strain amplification of about a factor of 5, but with about a 1000-fold decrease in load carrying capability.
To meet the requirements described above, more efficient actuators that combine high energy density (for compactness) with moderate strain amplification (for matching to moderate mechanical impedance loads) are required.
Accordingly, it is an object of the present invention to provide a piezoelectric actuator which overcomes the disadvantages of the prior art.
It is another object of the invention to provide a linear piezoelectric actuator which can be more economically fabricated than those found in the prior art.
It is yet another object of the invention to provide a linear piezoelectric actuator which combines high displacement with moderate to high actuation force.
It is still another object of the invention to provide a moderate displacement linear piezoelectric actuator having high actuation force.
It is a further object of the invention to provide net-shape forming techniques for readily and economically fabricating a linear piezoelectric actuator.